The present disclosure relates to a process for manufacturing fiber expansion joints. In particular, the present disclosure relates to a method for introducing fine particles of bituminous material, such as asphalt, into a slurry fiber mixture for formation into boards used in fiber expansion joint applications. Although the term “asphalt” is used throughout the present disclosure, it should be understood that any bituminous material, including tars and pitches, may be employed and still remain within the scope of the present disclosure.
Asphalt impregnated expansion joints are used in connection with concrete structures to relieve stresses created by thermal expansion and contraction of the concrete and prevent failure of the concrete caused by changes in ambient temperature. Typical applications for asphalt impregnated fiber expansion joints include sidewalks, driveways, floor slabs, streets, highways, airport runways, and similar applications. Because such concrete expansion joints are installed in applications exposed to the weather, it is desirable that water absorption be limited to prevent degradation of the expansion joint. It is also desirable that concrete expansion joints have strength and resiliency. Therefore, asphalt impregnated fiberboard expansion joints are required to meet or exceed the requirements of ASTM Standard Specification D 1751-04.
ASTM D 1751-04 requires that an expansion joint for concrete paving and structural applications have specified material characteristics, including that 35% weight of the finished fiberboard shall be asphalt uniformly distributed throughout the board. Additionally, the stress required to compress a test specimen of a fiber expansion joint to 50% of its original thickness must not be less than 100 psi nor greater than 750 psi. When a fiber expansion joint is compressed to 50% of its original thickness having three of its edges restrained, the amount of extrusion of the free edge cannot exceed 0.25 inch. A fiber expansion joint that has been compressed to 50% of its original thickness must recover at least 70% of its thickness within 10 minutes after the applied load is released. A fiber expansion joint must not have a density less than 19 lb./cu. ft. A fiber expansion joint test specimen with four square-cut edges, when submerged horizontally under 1 inch of water at 70 degrees F. may not absorb more than 15 volume % in 24 hours for a nominal volume of ½ inch and no more than 20 volume % for all other thicknesses.
Fiber expansion joints have been made by saturating fiberboard in an asphalt/solvent solution, allowing the asphalt solvent mixture to be absorbed into the fibers, and allowing the solvent to evaporate. Fiber expansion joints have also been made by adding solid asphalt particles into a slurry of fibers. The asphalt particles are dispersed in the fiber slurry by mechanical mixing, and the slurry is dewatered, pressed into a board and dried.